Change Set for U.S. Role in World

Updated Jan. 2, 2008 12:01 a.m. ET

When Iowa voters walk into their state's caucuses Thursday night, they will be kicking off a milestone campaign year that promises a new political course for America -- a course that could change its role in the world.

For the first time in 80 years, no incumbent president or vice president from either party is seeking the White House, creating an unusually unsettled campaign with no obvious front-runner. Power in Congress is divided so evenly between the two parties that neither has really been in control since the 2006...